It is common practice to conduct fine patterning by photolithography (hereinafter simply referred to as “lithography”) in manufacturing of semiconductor devices. The lithography is a process of applying a film of a photosensitive material (called “photoresist”; hereinafter simply referred to as “resist”) to a substrate, exposing the resist film to high-energy irradiation through a patterned photomask and transferring the resist onto a surface of the substrate according to the shape of the pattern of the photomask. In the lithography, the development of the resist is a technique of forming a fine resist pattern on the substrate due to a difference in developer solubility between exposed and unexposed portions of the resist film.
It is often the case to use inorganic substrates made of inorganic materials such as silicon single crystal in the lithography for manufacturing of semiconductor devices. However, there are cases that resist patterns are formed on organic materials such as organic polymer films, organic polymer substrates or organic coatings applied to substrates. It is herein noted that, in the present invention, the term “organic polymer substrates” refers to substrates made using, as raw materials, compounds (called “polymers”) obtained by polymerization of organic molecules. Typical examples of the organic polymer substrates are those made from polyethylene terephthalate (hereinafter sometimes called “PET”) as PET substrates.
In the case of forming resist films on such organic materials with the use of the same resist solvents as those commonly used for the application of resists by a wet application process to inorganic materials such as glass substrates, however, there occurs wetting of the organic materials, that is, swelling or dissolution of the organic materials by the solvent so that fine resist patterns cannot be formed on the organic materials due to loss of substrate surface uniformity.
As other processes for forming patterns on substrates, there are known a process using a photosensitive resist film, an ink jet process and the like.
The process using the photosensitive resist film is a process for forming a resist pattern by adhering the photosensitive resist film (hereinafter sometimes called “dry film resist”) to a substrate and exposing the dry film resist to ultraviolet irradiation. The dry film resist is commercially available under the trade name of e.g. “SUNFORT” from Asahi Kasei E-Materials Corporation, “ALPHO” from Nichigo-Morton Co., Ltd. or the like. In the process using the photosensitive resist film, it is desirable to roughen a surface of the substrate by sandblasting etc., before adhering the dry film resist to the substrate, for the purpose of improving the adhesion of the dry film resist to the substrate. However, such roughening of the substrate surface becomes a cause of pattern accuracy deterioration in the case of laminating a plurality of resist films and repeating fine patterning. Further, the dry film resist is generally adhered to the substrate by heating the dry film resist. In the case of using an organic polymer substrate as the substrate, such heating of the dry film resist leads to a large difference between dimensional changes of the dry film resist and the substrate due to a difference in thermal expansion coefficient between the dry resist film and the substrate and thereby makes it difficult to conduct accurate positioning of the dry film resist and the substrate.
The ink jet process is a process for directly forming a pattern by ejecting droplets of ink etc. onto a substrate. As compared to the lithography, it is difficult and time-consuming by the ink jet process to form an accurate pattern on a large area for production of large-sized displays even though the ink jet process is useful for production of small-sized displays.
There have been researched resist compositions for the application of resist films by a wet application process onto low-solvent-resistant organic materials in the field of lithography.
For example, Patent Documents 1 to 3 each disclose a resist composition using, as a resist solvent, an ether, long-chain alcohol or fluorinated alcohol solvent that is less likely to cause swelling or dissolution of low-solvent-resistant organic materials. In Patent Documents 1 to 3, however, there are no considerations given to the solvent resistance of the resulting resist pattern so that the resist pattern does not show sufficient solvent resistance.
Further, it is conceivable to conduct double exposure for finer resist patterning. The double exposure is a technique of patterning a resist film on a substrate by photolithography, forming another resist film with the application of a resist solution on the resist pattern, and then, again patterning the resist film. In such double exposure, the solvent resistance of the resist pattern is particularly important.
Patent Document 4 proposes, as a technique for solvent resistance improvements of a resist film and a resist pattern, a process for obtaining a high-solvent-resistant pattern by forming a cross-linking structure in a resin film, exposing the resist film to high-energy irradiation such as ultraviolet irradiation or electron beam so as to cause cleavage of the cross-linking structure in exposed portions of the resin film, and then, developing the exposed portions by dissolving in a developer. In this proposed process, however, the solvent used is the same as those commonly used for inorganic substrates and is not of the kind that does not cause wetting of organic materials.